An important parameter by which telecommunications apparatus are measured is the ability to restore traffic quickly in the event of a fault. This is normally achieved by protection switching. A protection switch is arranged to select one of, typically, two available inputs. When an input is selected, the traffic received on that input is passed on by the protection switch. When a fault is detected in respect of the selected input, the protection switch selects the other available input. Moreover, it is common for telecommunications apparatus to comprise more than one layer of protection switching. As a result, the connections between respective inputs and outputs of a telecommunications apparatus may depend on the respective settings of more than one protection switch.
Telecommunications apparatus is becoming increasingly complicated and are typically required to handle a very large number, typically thousands, of input and output traffic data signals. Accordingly, a typical telecommunications apparatus may be required to implement thousands of protection switches. The respective settings of these protection switches must be determined before the connections between the inputs and outputs of the telecommunications apparatus can be configured.
A problem here is that, in order to conform with industry standards such as ITU-T (International Telecommunications Union Telecommunications Standardization Sector) and Telcordia standards and customer expectations, protection switching must be performed within relatively strict time limits. Moreover, these time limits are expected to be met irrespective of the number of switching operations that need to be implemented. It is thus becoming increasingly difficult to perform the necessary switching operations, determine the setting of the protection switches and configure the connections between inputs and outputs within the time limits stipulated by industry standards.
This is a particular problem where it is desired to implement the required switching operations in a single core or microchip (sometimes referred to a single stage switch or monolithic switch). In such a switch, all of the necessary switching operations are performed in a single stage normally under the control of computer software. The computer software therefore tends to be relatively complex and slow.